Process and apparatus for dewaxing oils



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PROCESS AND APPARATUS FOR DEWAXING OILS mmm Filed 22, 1954 2Sheets-Sheet l AI Z .Z Lnmbmob, www NS w@ www Rf. MSGQ NS m2 MumNSm mwN@SEN W W a SN Q um LSE@ mw EN o2m NSS P. NW. www W .3v ww D 0 mm mm NSSam@ E A: G

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- .UNITEDL STATES] I PATENT OFFICE Pnocns's AND APPAIgUs non nEwAxmGDavid R. Merrill, Long Beach, Calif.,

assigner to Union Oil Company of California, Los Angeles, vCali1?.,acorporation'of California Application May `22, 1934. serial No. 'izasss'2a claims. (c1. s2-17o) trolled precipitation of the wax from thewaxcontaining stocks.

` In lubricating stocks, especially those of considerable Viscosityrange or boiling range, there will normally be present waxes varyingwidely in characteristics comprising at, the one extreme,

hard waxes of relatively high melting point, such as, for example, 150F. and at the other extreme,

' p soft waxes of relatively low melting point, such to dilute the oiLas, for example, 110 F. Although ordinarily only a small proportion ofthe total wax content in .the lubrica'tingkoil stock will consist ofhard waxes, their presence in the waxy stock is very limportant sincethey have such a. low solubility in the solution Vof waxy oil anddiluent and are usually the iirst type of wax to separate onl gradualcooling.

- Also because of the low initial concentration in the solution suchhard waxes are precipitated in a very nely divided form on excessivelyrapid show little tendency towards resolution of these iine particlesand crystal growth. -It'is, therefore, evident that the most criticaltemperature range is that in which the initial separation of wax occursbecause if an excessivel number of nuclei are formed at this time thereis little possibility of correcting this situation by subsequentdigesting operations. It is an object of my invention to control theformation of nuclei during the initial stages of wax separation so as toprevent formation of an excessive number of such nuclei and to permitfurther crystal growth on nuclei formed in the. early stages ofchilling.

In general, crystallization of wax is accomplished by inducing asupersaturated condition in the solution of waxy oil and solventemployed This is accomplished either by increasing the concentrationofthe solute by vaporization orseparation of solvent, or by reduc-A ingvthe solubility by cooling, or both. Some investigators have shown thereis a narrow range of concentration and a corresponding range oftemperature of supersaturation within which free formation of newcrystal nuclei will not'occurv. In this range of supersaturation,crystallization will occur on nuclei already present but formation ofnew nuclei will 'occur toonly a very lim-,-

. range of supersaturation is the production of lubricating oils pane.

phase.

ited extent, if at all. This range `o supersaturation is commonlyreferred to as the metastable range. For purposes of deiinition,` themetastable that range of supersaturation within which' crystallizationoccurs on 5 the surfaces of crystals already present and spontaneousformation of new crystal nuclei in large amount does not occur.

As soon as'the metastable range of supersaturation is exceeded, however,a so-called labile range of supersaturation is reached in which rapidformation of new crystal nuclei will occur. Thus, the labile range ofsupersaturation denotes" a degrec of supersaturation inV whichspontaneous formation of lnew large extent. With a slow rate ofchilling, the rate of crystallization upon'the wax nuclei alreadypresent is suiciently rapid to -relieve the supersaturation and permitcrystallization to occur within the metastable range so thatuncontrolled formation of new nuclei does not occur. With an excessivelyrapid rate of chilling, however, the degree of supersaturation exceedsthe metastable range and this results in the formation of large numbersof new nucleiand conse- 25.

quent reduction in the average particle size due to the production of alarge amount of ne particles which are of a gelatinous or slimycharacter. A wax slurry of this characteris diicult to separate from theoil solvent solution by either settling or filtering. The permissiblerate of chilling will, of course, depend not only on the extent of themetastable range but also upon the rate at which supersaturation isrelieved by crystallization upon particles of wax .already present. Itis another object of my invention to control conditions and rate ofchilling in dewaxing operations within the metastable range ofsupersaturation and to relieve supersaturation by crys-. tallization ofwax on wax particles already present in the solution.

In. one of the known methods fonseparating' wax from oils, the oil ismixed with a hydrocarbon solvent, more particularly-a. liquefiednormally gaseous hydrocarbon solvent, such as liquid pro- The admixtureis eected under a pressure suilicient to maintain the solvent in theliquid Thereafter, a portion of the solvent is` vaporized under reducedpressure inorder to eiect chilling and precipitation of wax fromsolution. In the case of propane, by reducing the vpressure down toatmospheric, a temperature of approximately 40 F. may be obtained in theremaining oil and solvent solution. The wax which precipitated duringthe chilling operation crystal nuclei occurs to avery 15` is thenremoved by settling, ltering or centrifuging. The remaining propane maythen be removed from the dewaxed oil by distillation.

In dewaxing lubricating oils by the use of.

liquefied normally gaseous hydrocarbons such as propane', it has beenfound that in batch operation the rate of chilling must be verycarefully controlled because when the chilling is accomplished at anexcessive rate, a wax slurry is formed which is very diiiicult toseparate from the oil and remaining solvent by such means as settling orfiltering. It is usually found undesirable to exceed a chilling rate ofabout .3 F. per minute in the temperature range from about thetemperature at which wax begins to precipitate from solution or thecloud point of the oil solution down to the final dewaxing temperature.However, more rapid chilling may more often be carried out between thetemperature ranges of 0 F. and the usual final temperature of about 40F. Preferably, however, the rate of chilling should not be more than 3F. per minute from the cloud Y point of the solution down to the finaltemperature of 40 F. While such control of chilling rate in bathoperations is relatively simple and can b'e accomplished readily inchilling by internal refrigeration merely by drawing oif the propanevapor at a suitably controlled rate so that the pressure of the vaporabove the liquid falls at a rate corresponding with the desired rate ofreduction of temperature, controlled chilling under the conditions ofcontinuous flow is more diiiicult to accomplish because it has usuallybeen necessary in the past to employ a definite number of stages withdefinite pressure differences between each stage. 'I'hese pressuredifferences correspond with definite differences in temperature and thetendency is for the temperature of the stream to drop immediately, dueto flash vaporization, as soon as the pressure is reduced on passagethrough the control Valve in the line connecting the stages. It is thusanother object of my invention to accomplish controlled chilling underconditions of continuous ow and to obtain results similar to controlledvaporization of solvent in batch chilling operations.

' Various other objects and features of my invention will becomeapparent to those skilled in the art from the following description ofmy invention taken from the drawings.

I have discovered that controlled chilling within the metastable rangeof supersaturation in'a continuous system may be effectivelyaccomplished by employing a plurality of chilling chambers operating atsucceedingly lower temperatures and in which the stream of enteringsolution of waxy oil and solvent to the first chiller and from onechiller to the next succeeding chiller is commingled with a considerableamount of colder recirculated solution from the chiller to which theentering stream is passed. The mixing is, for example, in the ratio of 9volumes of recirculated solution to one of the entering stream. By rapidmixing and thorough agitation of the entering stream and therecirculated stream, cooling of the entering stream is accomplished bymixing with concurrent reduction of the wax content by dilution ratherthan by vaporization of propane under reduced pressure, so that themetastable range of supersaturation is not exceeded at any time. Ofcourse, the chillers in the series are maintained at successively lowertemperatures by vaporizat-ion of propane at successively lower pressuresbut the actual chilling of the entering stream is accomplished by mixingwith colder recirculated solution.

The combined streams are introduced into the bottom of the respectivechillers and as the mixture flows up the chiller, the temperature isreduced by lessening of hydrostatic head at a rate not in excess ofabout 3 per minute.

The process will be more readily understood by the following descriptiontaken from the drawings in which:

Fig. 1 represents a general flow diagram of arrangement of apparatusadapted to carry out my process;

Fig. 2 represents a modification of arrangement of chillers adapted tocarry out the process, and

Fig. 3 represents another .modification of a series of 'chillersprovided with a schedule of differentpumps to prevent breakingV down ofwax crystals by attrition as will be set forth in detail.

`Referring to Fig. l, a wax-containing oil such as an S. A. E. i0 waxydistillate produced from Santa Fe Springs crude oil is taken from tank Iand is passed Via line 2 to pump 3 which forces the oil through line 4and heater 5 and then via line 6 into line 1 where it meets a stream ofliquefied normally gaseous hydrocarbon solvent such as liquid propanewhich has been Withdrawn from tank 8 via lines 9 and I0 and pump Il.Approximatelyv4 to 6 volumes of propane are mixed with one volume of thewaxy oil. The waxy oil and liquid propane brought together by means ofseparate pumps 'are passed through mixer I2 and thence through heatinterchanger I4, line I5, and heater I6 where the temperature of thesolution is raised to that at which the wax is completely in solutionas, for example, F.' The mixture then passes via line I1 through heatinterchanger I8, line I9 and cooler 20 where the solution is cooled downto a temperature which is definitely above the temperature of theinitial separation of wax although preferably the temperature may bereduced to approximately a few degrees above the cloud point of theoil-diluent mixture. Pressure is controlled by means of relief valve 22on line 2|. This valve is employed for the purpose of maintainingsuflicient pressure in the heater I6 to prevent flashing in the heater.

The combined stream of oil and propane is then led into the bottom ofthe first of the series of chillers 23, 23a, 23h and 23o operating atsuccessively lower temperatures. Prior to the introduction of themixture into the first of the series of chillers, it is commingled withrecirculated chilled oil and propane from the top of chiller 23 which iscirculated via line 24 by pump 25. The resultant mixture then flowsthrough 26 into the bottom of chiller 23. upper part of this chiller aswell as in the succeeding chillers operating at successively lowertemperatures is maintained constant by maintaining a constant pressurein the propane vapor leaving them. Recirculation from the chiller isdesirably accomplished in the ratio of about 9 volumes of recirculated'solution to one volume of the entering solution so that the waxconcentration in the mixture entering the chiller does not exceed themetastable range of supersaturation. It will be observed that thecombined stream is introduced into the chiller at or near the bottom sothat there is little or no evolutionof vapor or flashing on entrance ofthe mixture into the chiller. The height of liquid at the point ofintroduction will preferably be such that its hydrostatic head is equalto the difference in the vvapor pressure of the solution at thetemperature of the entering The temperature in the mixture. and at thetop when the solution at the top is in equilibrium with propane at thepressure normally maintained in the chiller. On continued circulation,the warm entering mixture will be -gradually cooled as it rises in thechiller due to the reduction in hydrostatic head and consequentevolution of vapor in conjunction with a certain amount oi mixing byeddy currents. 'The chiller will be preferably of such size thatthevolume of the up-iiowing stream will be suiiicient so that the desiredcooling rate of for example, about 3 F.

per minute, will not be exceeded.. I

Upon reaching the top of the ilrst chiller, the

Y solution ows down through line 39 and valve 3| which is actuated by afloat control 32 in the first chamber. It will be noted ,that this valveis located at a low level so that the distance from the valve to themixer is very short and ashing upon passage through the valve is reducedto a minimum by immediate mixing and consequent cooling of the stream.Upon passage through valve 3| the partially chilled solution-isimmediately commingled with colder solution from the top of the secondchiller' 23a circulated via line 24 and pump 25 in exactly the samemanneras in the iirst chilling chamber. 'I'he mixture is then introducedinto the bottom of the second chiller vla line 26. Chilling in chiller23a is exactly-the same as in chiller 23 except that temperature andpressure conditions are lower. Likewise, the operationin the subsequentlchillers 23h and 23e is similar to that in the previous chillers. It isapparent that the number of chilling stages provided should besufllcleutrthat the chilled salu-f tion leaving the top of the lastchiller will be.; at the desired dewaxing temperature as, for example,40 F. When the oil being chilled does not contain suiiicie'nt propane toaccomplish' the desired chilling, further quantities may be `introducedthrough lines 38a controlled by valves y The pressure at the top of eachchiller 23, 23a, 23h and 23e is controlled by compressors 35, 35a, 35hand 35e. The propane vapors from the various chillers are removed fromthe chillers via line 33 which pass to compressors 35, 35a, 35h

and 35e where the vapors are compressed'and trolled by float controlvalve 4| by means of pump 42 which forces the mixture towax separatingdevices such` as settlers, illters, centrifuges or other mechanical waxseparating units. In the drawings, the chilled mass is passed into thevapor tight wax separator or settler 43. Make-up propane at 49 F. may beintroduced into the chilled oil via line controlled by valve 45 in orderto provide ior adequate settling or iltration of the precipitated wax.In order to prevent ebullition or boiling in the wax separator duringthe wax settling operation, pressure is imposed upon the solution ofoil. This is accom- .plished by maintaining pressure within theseparator by pump 42. As the chilled mass in the wax separator remainsin a non-ebullient state, the wax settles out and is collected yby vanes46 on shaft 41 which is operated by belt 48 connected to a suitablesource of power not shown. The

`ferred temperature of 40 F. via line 49 containing the remainingvpropane is collecting tank A59. The precipitated wax slurry containingpropane settling at the bottom of the wax separator 43 isremoved throughline 5| and pumpedby pump 52 into line 53'where it meets a'stream ofchilled recovered oil and propane from surge tank 54 via line 55 andpump.56: The

two streams then pass through line 53 and mixer x 51 into settlerV 58which is constructed Similarly to vsettler- 43 and in which the waxi'rom settler 43 is washed -with the lilute'oil-propane solution fromsurge tank 54. Oil and propane separated from thev wax slurry iswithdrawn via line 59 and passed into collecting tank 59.

The once washed wax slurry is withdrawn from the bottom of settler 59vialine 69 by pump 6| which forces the wax slurry through line 62 where'it meets a stream oi' chilled propane at 49 F.

coming from chilled propane storage tank 93 via line 64, pump 65, line61 and valve 68. The mixturethen flows through mixing coil' 69 intoanother rsettler 19 constructed similarly to settlers 43 and 58. Insettler 19 the wax from settler 59 is washer withV fresh chilled propaneand. any oil separated is withdrawn together with the chilled propanevia line 1| and passed into surge tank 54. As stated previously, thissolution containing a small amount of recovered oil is employed to washthe wax slurry from the` rst settler 43. The countercurrent Washing'steps may be carried on in as many stages as desired. The chilledpropane in tank 6 3 is produced bywithdrawing a portion of the'propaneunder pressure from tank 8 via lines 9 and 12, cooling it in heatinterchang ers 13 and 14 and passing it into tank 63. The

vpropane m sa ls chilled to 40 ruby vaporizlng a portion through line 15and compressor 19 which forces the vaporized propane through line11coo1er 36, line 31 into propane storage .tank l.

The substantially oil-free wax is 'withdrawn' from the bottom of settler19 via line 99 by pumpl 8| which forces the wax through line 32, heatin-A terchanger 83. line 94 into high. pressure exhauster wherevaporized propane under high pressure is Withdrawn via line 86 into line81. Wax in exhauster 85 is continuously recirculated, from the bottominto the top of the exhauster via line 99, pump 89, line 99, heater 9|and line 92. 'I'he Wax or a portion thereof is then passed throughvalvey 3" .wax-free oil dissolved in propane` is withdrawn4from'separator 43 via line 49 and is passed into 93, line 94, heater95, line 96 into the'low pressure exhauster 91. `Vaporiaed propane underlow pressure is withdrawn via line 98, compressed in compressor 99 andpassed into line 91. Wax in low pressure exhauster 91 is recirculatedvia line |99,-

pump |9 I, valve |92, line 94, heater 95 and line 96. Substantiallypropane-free wax is withdrawn through valve |93 and passedthrough.coo.er..|94, line |95 into waxstorage tank |96where it ismaintained melted by steam circulatedv through coil |91.

The substantially wax-free oil and propaneV from collectingtank 59 iswithdrawn via line ||9 f and'pumped by pump through line ||2, heatinterchanger ||4, line ||5, valve ||6'into high vpressure exhauster 1wherevaporirled propane underhigh pressure is withdrawn via line. H9.The oil in high pressure exhauster |'|1'is continuouslyrecirculatedthrough line I9, pump 29, line |2|, heater |22 and linev |23. 'gde oilconen passed through valve'l24, line |25, heater |29, line |21 into lowpressure exhauster |29. Propane and oil from the low pressure exhausteris continuously relrculdted through une m. pump m.valve nl,

line |25, heater |26, line |21 into exhauster |28. Vaporized propaneunder low pressure is withdrawn from low pressure exhauster via line |32and passed into line 98, compressed in 99 and passed into line 81.Substantially propane-free oil is withdrawn from the low pressureexhauster vla line |29, pump |30, valve |33, line |34 and passed intostorage tank |35 which is cooled by cooling coil |36. The propaneVaporized from the low and high pressure exhausters and passing throughlines 81 and I8 is passed into lines |31, 11, cooler 36, line 31 intopropane storage tank 8.

In the foregoing disclosure, I have described a method for chilling oilto precipitate wax wherein the stream of waxy oil and propane solutionafter cooling to a temperature slightly above that of initial separationof wax is introduced under conditions of thorough mixing into a muchlarger stream of propane-oil solution at a considerably lowertemperature at which temperature it is saturated but not appreciablysupersaturated with wax and carries in suspension wax particles. Therelation between the temperatures and Volumes of the two streams ispreferably such that the increase in temperature of the circulatedstream and consequent increase in solubility of wax in the propanesolution is substantially sumcient to hold in solution the quantity ofvwax brought in by the entering stream. In other Words, operatingconditions will preferably be chosen so that the wax concentration insolution in the combined stream corresponds approximately with thesolubility of wax in the solution at the temperature of the combinedstream and will certainly be chosen so that any supersaturation will bevery minor in extent and within the metastable range.

'I'he amount of recirculation required in each stage for production ofavwax slurry containing the wax in coarse crystals so as to be readilyremovable by settling or filtration will depend primarily upon thenumber of stages of chilling provided or, in other words, upon thedifference in temperature between stages. With a larger number of stagesor smaller difference in temperature, less recirculation of liquid willbe required. Other factors which influence the amount of recirculationrequired in any particular case are the extent to which supersaturationis reduced in the circulating stream prior to mixing with the incomingsolution and the concentration of wax in the incoming solution asinfluenced by the amount of dilution of the waxy oil with propane orother diluent. In general, it is necessary in the practice of myinvention to choose such conditions of recirculation as will result inthe wax' concentration in the mixed stream not exceeding the metastablerange of supersaturation of wax at the temperature of the stream. Theextent of this metastable range of supersaturation will in turn dependupon such factors as the character and quantity of wax in the waxy oil,the concentration of oil in the solution as influencing the solventpower of the propane for wax, and the presence in the solution ofcolloidalimpurities which ordinarily tend to reduce the crystallizationrate or modify the crystal habit. Such impurities may be asphaltic ymetastable range may be determined by chillingv the solution at Ivaryingrates and determining the rate at which uncontrolled formation of newnuclei occurs and hence at that rate of chilling, the degree ofsupersaturation exceeds the metastable range. At some lower rate ofchilling' where large crystals of wax are formed, the supersaturationwill be found not to exceed the metastable range.

The four steps shown to chill the oil are possibly not the minimumpermissible in all cases but should be suiiicient for most cases. Forexample, when it is desired to chill the oil-propane solution from 90down to 40 F., the oil-propane solution in line 2| at a temperature of90 F. and under a pressure of 153 lbs. gauge is mixed with 9 volumes ofcolder solution at 60 F. recirculated from the ilrst chilling column.The combined mixture will have a temperature of 63 F. when introducedinto the bottom of the chiller 23. As the combined stream flows upthrough the chiller, the lessening of the hydrostatic head permitsvaporiz-ationof a portion of the propane which cools the oil from 63 F.at the bottom to 60 F. at the top.

The chiller is preferably of such size that the volume of the up-flowingstream will be suflicient so that the desired cooling rate, for example3 F. per minute, will not be exceeded. It is evident that with arecirculation of 9 volumes of recirculated material to one volume ofentering stream and with a temperature differential of 3 F. between thebottom and the top of the chiller, the volume of up-ilow shouldapproximately correspond to ten minutes ,flow of the entering stream.Pressure is maintained at the top of the chiller at about 97 lbs. gaugeby operation of compressor 35. 'I'he operation of chiller 23a is exactlythe same as that in chiller 23 except that it is maint-aimed at a lowertemperature level, for example, the mixture withdrawn from the top ofthe chiller 23 at a temperature oi 63 F. is commingled with 9 volumes ofrecirculated material from chiller 23a at a temperature 'ot 30 F. Thecombined stream will havea temperature corresponding to 33 F. As thehydrostatic head on the mixture in 23a is reduced, vaporization ofpropane will gradually reduce the temperature to 30 F. at the top of thechiller.

Pressure is controlled in 23a by compressor 35a which maintains apressure in the chiller at about 55 lbs. gauge. In chiller 23h materialfrom the top of chiller 23a at 30 F. is commingled with 9 volumes ofrecirculated material from the top Aof chiller 23b at a temperature of 0F. to produce a combined stream at a temperature of 3 F. which isreduced by flowing up through the chiller 23h to 0 F. A pressure ofabout 27 lbs. gauge is imposed on chiller 23h by means of compressor35h. In the next chiller, 23e, one volume of 0 F. material from the topof chiller 23h is commingled with 9 volumes of F. material from the topof chiller 23e, producing a combined stream having a temperature of 36F. which is reduced at the tcp of the chiller to approximately -40 F. byvaporization of propane at the reduced hydrostatic head. The pressuremaintained at the top of gauge with theentering stream. In Fig. 2, Ihave shown a modiiication for accomplishing the aboveresulta It will beobserved that Fig. 2 merely represents a series of chilling. chambers.However, it'will be understood that apparatus for propane with waxy oilvand for preparing the mixture prior ,to introduction into the chillingchambers is similar to that described ,in Fig. l. Likewise, theapparatus-for separating vpropane from. the separated oil and waxfractions and for recovering propane may be carried-on similarly to thatdescribed 'for Fig. l. l

Referring to Fig. 2, it will be observed that each 'chiller comprises avertical column as the chillers shown in Fig.. 1, except that it iscenntrally divided by a vertical partition or baille 21 extending almost tothe top of the column which dividesv the chiller intotwo sections 28 and29. At the lower portion of the partition, an injector 38 is providedwhich permits iiuid iromsection-28 and line 2| to passh into section 29.Injector 38 is provided with bailies 38 in section 29 so that 'mixing ofthe two streams' is promotedbefore discharge into section 29.

must be so' thorough and the The enterlngstreamcf propane and waxy oili'rom line 2| `passing through relief valve 22 passes through theentrance nozzle 39 which is lprovided with insulating sleeve `39 inorder to` prevent appreciable cooling of the entering stream bysurrounding-cold solution. and accom- 'panying deposition ofwaxonthewalls of the nozzle. 'I'he entering stream is injected into the injector38 and is commlugledl with approximately 9 volumes'of chilled solutiondrawn into the injector from Asection 28. The mixture passingthrough'the injector 38 and bailles A38' is lintroduced. into the lowerportion of sectionl 29. As the combined stream ows up section 29, thetemperature is lowered approximately 3 by vaporization of propane due tothe reduction in hydrostatic head. The mixture overows overV4 partitionwall 21 into chamber 28 where it is recirculated to the injector, parto1' the solution bein withdrawn via'line 30. Thus,'by providing. aninjector I may produce circulation of the mixture within the chiller.The agitation mixing so rapid that no vopportunity is aiorded forcooling of the incoming stream by conduction-of .heat to the circulatingstream but the cooling. should take place only by actual mixing ci.' thetwo streams, since otherwise, the supersaturation may readily exceedthe-metastable range'. In practice this mixing may be accomplished morereadily lay-employing multiple iets rather than the simple jet injecrshown.

fThe Vrtially chilled mixture is withdrawn from thebottom of'section 28vvialine 30 and lower temperatures.- sure conditions inthe chiller willbe exactly the pump 25 and passes through float control valve 3| intothe `next chiller. The operation in chiller 23a and in vsubsequentstages 23h and 23el is exthesame asin' the rst chiller 2 3 except thatthe chillersare maintained at' successively f The temperature andpressame "as in the .case of .external recirculation xample,`if it isdsil'edl'to' the top of 'the chamber. A pressure of 97 f solution in theiirst chiller, for tain a relatively limited number o1' nuclei and thechill oil from .90 F. to 40 F., the entering stream at 90 F. underpressure of 153 lbs. gauge is commingled with 9- volumes ofV 60.material in inJector 38, the-combined stream having a temperature of 63which is reduced to 601b s. gauge ismaintained in 'chiller '23 bycompressor 35. Material withdrawn from the bottom of section- 28 of.chiller 23 at 60 F. is commingled with 9 volumes of v30 F. material inthe injector 10 of chiller 23a to produce a combined mixture of 23 F.material which is reduced at the top of the chiller to 30 F. A pressureof 55 lbs. gauge'is maintained in chiller v23a by compressor a.Likewise, material at 30 the bottom of the chiller 23a is commingledlwith 9 volumes -of 0 F. material .at the bottom o! section 28 of chiller23h to produce a mixture of 3 F. material in section 29 which is reducedto 0 F. at the top of the of 27 lbs. gauge is maintained in chiller 23hby compressor 35h. 0 F.materlal withdrawn from the bottom of chiller 23his commlngled with 9 volumes of F. material at the bottom of F.withdrawn from l5 chiller. A pressure 20 section 28 of chiller 23e toproduce a mixture 25 or 36 F.' which is reducedat the tcp of the chiller23cto 40 F. A `pressure of 0 lbs. gauge vis maintained in chiller 23e bycompressor 35e.

The chilled solution containing precipitated cipitated wax is separatedfrom the oil and remaining propane.

Operation oi the chillers is best started by lling all or thechillerswith the propane-waxyoil solution at a temperaturev above thetemperature of initial separation of wax and then cooling each wax iswithdrawn from section 28 oi' the last 80 Achiller very slowly bydrawing'off propane vapors o at a controlled rate so thatcrystallization will occur slowly and relatively large crystals will bel formed. After proper temperatures are attained in each chiller, thecontinuousv flow may be started. Under these conditions,

example, will contendency will be for crystallization to occur on thesenuclei already present ratherthan for new the circulating nuclei to beformed. On continued operation, the

nuclei will tend'to be carried on in the succeedlng chillers and thenumber of nuclei in suspensionin the rst chiller will be reduced.However, fortuitous formation of nuclei by local excess chilling or byattrition will keep the proportion 58 oi.' nuclei in suspe on at asuitable point. This tends to be self-re ating'since if the proportionoi nuclei is unduly decreased, the rate at which supersaturation will berelieved will be reduced and there will be a greater tendency for thesuper- .60

saturation to enter the labile range with formation oiadditional nuclei.The reduction in the number of nuclei by flowing into succeeding stagesis very` desirable, las it will tend to promote the formation of largercrystals the subsequent settling or ltering operation.

'One V of the most essential points for successi'ul operation is theimmediate and complete mixing of the two streams, that is, the enteringstream and the colder recirculating and 70 the avoidance of anyappreciable cooling of the entering stream in any manner except bymixing with the circulating stream. cooling or the en# .l tering'streamby conduction oi 'heat' to the ciri' 'culating stream or bypartial vaporization is par- 7l which will facilitate ticularly to beavoided. While it is possible that by the use of injector types ofmixing devices, 'mixing can be accomplished so quickly as to preventappreciable iiashing of the entering stream on release of pressure atthe entering nozzle or orifice, such avoidance of fiashing may at timesbe diflicult to `accomplish in practice and in this latter case it isproposed to prevent flashing by maintaining a sufiicient pressure uponthe combined streams during the mixing operation so that any possibilityof iiashing is obviated.

The maintenance of a higher pressure at the point of mixing will, ofcourse, necessitate the release of the pressure at a later point inorder that vaporization may take place in the chiller at the desiredtemperature. The release of the pressure by passage through a reliefvalve or orifice will result in the setting up of shearing stresses inthe iiowing liquid which may cause appreciable attrition of the waxparticles in suspension with consequent formation of additional nucleiand general reduction of particle size of wax. Moreover, the release ofthe pressure through a valve or orifice will result in dissipation ofthe energy corresponding with the pressure differential in the form ofheat. With ,the recirculation of, for example, 9 volumes for one volume'of entering solution, the energy so dissipated would be appreciable andthe heat generated would increase the load on the refrigerating system.In Fig. 3 I have disclosed an arrangement of apparatus wherein theenergy corresponding with the pressure drop may be converted back intomechanical energy as by -passage, of the solution through a positivedisplacement pump, such as a gear, Kinney, Waterous or reciprocatingpump. I f desired, the mechanical energy may be converted intoelectrical energy and the electrical energy may be returned to the line.In this way any undue increase in the refrigeration load is avoided.Moreover, by suitable choice of the type of pump, the breaking down ofthe wax crystals by attrition is reduced to a minimum.

Referring more particularly to Fig. 3, .the waxy oil solution in propaneprepared in they manner disclosed in Fig. 1 and passing through line 2|is introduced into injector |50 where it is commingled with coldersolution from chiller 23, for example, in the ratio of 9 volumes ofrecirculated solution to one volume of' the entering solution andcirculated from chiller 23 via line 24 and circulating pump 25. Themixture then flows through mixing coil |5|, and passes through apositive displacement pump |52 from which the combined streams fiowthrough line |53 into section 29 of chiller 23. Chiller 23 is preferablydivided into two sections `28 and 29 by' vertical baffle 21, theupperportion of the chiller being open to permit flow of'v liquid fromsection 29 into section 28. 'I'he operation and flow of liquid inchiller 23 is exactly the same as that in the chillers disclosed in Fig.2 except that the injector in the interior of the chiller is omitted,circulation being accomplished externally in. the manner up by pump |55which comprises a positive displacement pump, the speed of which iscontrolled by float control 32. The solution picked up by pump |55 ispassed by line 2|a into injector lilla where it is commingled withcolder solution from section 28a circulating via'line 24a andpump 25a.Combined streams pass through mixer I5 a, pump |520, line |53a intosection 29a of chiller 23a.

" scribed for Fig. 1.

A portion of the chilled solution` from section 23a passing through line24a is by-passed through line |54a to pump |55a controlled by iioatcontrol 32a which is forced through line 2lb to further chilling in amanner similar to that described for chillers 23 and 23a, or it may bepassed to wax settling or filtration in order to separate precipitatedwax from solution in the manner dethe chillers 23 and 23a is controlledby compressors 35 and 35a. Propane vaporized from the chillers iswithdrawn via lines 33 and 33a, compressed in compressors 35 andv 35aand passed into manifold 34 from which it may be passed to the propanecondenserand recovered in a manner described in Fig. 1.

Thus, in Fig. 3, I have described the method of operation by which allvalves with accompanying possibility of attrition of wax crystals isavoided and the flow is controlled by speed control of positivedisplacement pumps. As stated above, pumps |55 and |55a comprisepositive displacement pumps with speed control by a float controldevice. Pumps 25 and 25a comprise constantspeed centrifugal pumps,preferably of slow speed type and pumps |52 and 52a comprise positivedisplacement pumps such as gear, Kinney, Waterous or reciprocating pumpswhich are connected to induction motors which, when over-driven, willreturn power to the line.

In the above schedule of pump types, instead of employing aconstant-speed centrifugal pump in the position indicated, for pumps 25and 25a, a positive displacement pump with speed control to maintain;constant pressure may be substituted therefor, pumps |52, |52a and |55,|55a remaining the same as in the above schedule. It is obvious to thoseskilled in the art that further modi-.

cations could be made in the types of pumps and methods of controlwithout departing from the spirit of the invention.

While I have described the use of liquid propane as the internalrefrigerant-diluent, itl may be observed that I may 'employ otherliquefied normally gaseous hydrocarbons for. this purpose. vSuchhydrocarbons include methane, ethane, propane, iso-butane, butane ormixtures thereof. These hydrocarbons may be obtained by rectification ofcasinghead gasoline by the so-called0 stabilizing method. They are theoverhead thus obtained. They are liquefied by compression and cooling inthe conventional manner and are drawn off into pressure chambers wherethey are maintained in the liquid state until they are used.

It is to be understood that the above description is merely illustrativeof preferred embodiments of my invention of which many variations may bemade by those skilled in the art without departing from theA spiritthereof.

I claim: v

1`. An apparatus for separating wax from oils which 'comprises means formixing waxy oil with a liquefied normally gaseous solvent, a pluralityof chillers, means connecting said Chillers to permit passage ofsolution from the top to the bot- The pressure at the top of y tom ofsuccessive chillers and.means for recirl Imaintaining said chillers atsuccessively lower means for' mixing waxy oil circulating to the bottomof said other compartment with oil entering said chiller and means forwithdrawing oil containing precipitated wax from `the bottom of saidother compartment.

5. An apparatus as in claim 4 in` which said means for circulating oiland for mixing entering oil with oil at the bottom of said othercompartment comprises an injector.

6. An apparatus for separating wax from oils which comprises a pluralityof chillers, a partition dividing the lower portion of each of saidchillersinto 'two compartments, an injector positioned at the bottom ofsaid chillers and compartition in said chiller,

municating from one compartment to th other,

means for passing oil from said chiller into said injector, meansconnecting the bottom of said chillers with successive chillef and meansfor maintaining said successive chillers at successively lowertemperatures.

7. An apparatus for separating wax from oil which comprises a verticalchiller, means in said chiller to divide thelower portion of saidvertical chiller into two vertical compartments, a mixer, means forpassing oil from the bottom vof one of said compartments to said mixer,means for passing oil to be chilled to said mixer, means' for passingthe combined streams from said mixer to the bottom of said othercompartment and a pump positioned on said last mentioned means.

8.` An apparatus for separating wax from oil which vcomprises a.vertical vchiller,- a vertical said partition dividing the lowerportion of said chiller into two'compertinents, a mixer, 'a conduitconnecting the bottom of one compartment with said mixer,l a

i conduit connecting said mixer with the bottom of said othercompartment, means for passing oil from the bottom of said rstmentionedcompartment to said mixer and from said mixer to the bottom ofsaid other compartment, said means comprising a pump-positionedintermediate said conduit connecting the bottom of `said first mentionedcompartment with said mixer,` means.

for passing oil to bechilled into said'mixer and means on said conduitfrom said mixerto. the

l bottom of said other compartment to vreduce the pressure of thecombined stream passing tosaid other compartment.`

9. A process for chilling liquids-which'comprises mixing'the liquid tobe vchilled with a volatile liquid refrigerant under superatmos?.

pheric pressure, commingling said mixture with a sulcient quantity of toreduce the temperature o1' the mixture to be chilled to substantiallythat oflthe previously chilled liquid and removingvaporized liquid re'frigerant. from the-combined mixtures 9 in which .the voladrant is aliquefied normally gaseous hydrocarbon.

10. A process asin claim s 11. A process as in claim -9 in which the`vola tile liquid refrigerant is liquid propane. chilling liquids whichcom- 12. A process for prises mixing the liquid to bechilled* with avolatile liquid ,refrigerantv under superatmosof the previously chilleds ing a portion of the volatile liquid refrigerant passing the mixturepreviously chilled liquid chamber connected in series 'to be chilled insuflcient quantities to reduce the temperature of the mixture to bechilled to substantially that of the chilled mixture withdrawn from thechilling chamber and 'vaporiz'lng a portion of the volatile liquidrefrigerant from 10 the chilling chamber' to chill the combined mixture.

13. A process as in claim 12 in which the temperature of the combinedmixture of liquid to be chilled, volatile liquid refrigerant and chilled15 liquid withdrawn from the chilling chamber is reduced tothetemperatureA of the withdrawn chilled liquid by lessening thehydrostatic head on said mixture.

14. In aV process for dewaxing oils the steps 20 comprising-mixing waxyoil with a volatile liquid y refrigerant under. supsratmosphericpressure, A commingling said mixture with a'suftlcient quantity ofpreviously chilled waxy oil to reduce the temperature of the'waxy oil tobe chilled to sub- 26 stantially that of the previously chilled waxyoil, and vaporizing a portion of the volatile liquid refrigerant fromthe combined mixtures.

15. In a process for dewaxing oils the steps comprising mixing waxy oilwith a. volatile liquid. 80 refrigerant under superatmospheric pressure,commingling said mixture with a suilicient quantity of previouslychilled wainr oil to reduce the/ temperature of the waxy oil to bechilled to approximately 3 F. higher waxy oil, and Vaporizfrom thecombined mixtures.; 16. A process as in claim 14 in which the volatileliquid refrigerant is a. liquefied normally 40 gaseous hydrocarbon.

17. A process as in claim 14 1in which the volatile liquid refrigerantis liquid propane.

18. In a process for d'ewaxing oils the steps comprising mixingwaxy'oiPwith a volatile liquid refrigerant under superatmosphericpressure. into the bottom of a chilling chamber which is maintained at'a lower pressure and at a lower 'temperature than said mixture,withdrawing chilled waxy oil and volatile liquid 50 refrigerant from thetop of the chilling chamber and mixing said withdrawn mixture with thewaxy oil and volatile liquid refrigerant to be s chilled in asuiil'cient quantity to reduce-'the tem.-

perature of the mixture to be chilled to substan- 66 tially thetemperature of the withdrawn chilled mixture and vaporizing al 'portionof the volatile liquid refrigerant from the combined mixtures.

19. A process as in claim 18 in which'the temperaturewf the combinedmixtures is reduced 60 to the temperature of the chilled waxy oil andvolatile liquid refrigerant withdrawn top of the chilling chamber.

2 0. In a process for dewaxing' oils the steps comprising mixing waxyoil with a volatile liquid refrigerant under superatmospheric pr'eure.

passing said mixture into thev bottom of chilling s and maintained atsuccessively y'lower temperature and pressure levels by vaporization ofsaid volatile liquid refrigerant under reduced pressure, withdrawingchilled mixture from' the top of said chilling chambers and comminglingsaid withdrawn mix- .ture with the 'mixture to be chilled entering` thebottom of said chilling chamber. said admix- 16 than the temperature 8 6from the l ture being in quantities suiicient tovreduce the .temperatureof the combined mixture to subxels by vaporizationof said volatileliquid. refrigerant under reduced pressure, withdrawing chilled mixturefrom the top of said chilling chambers and commingling said withdrawnmixture with the mixture to be chilled entering the bottom of saidchilling chambers said admixture being in quantities suicient to reducethe temperature of the combined mixture to substantially the temperatureof the chilled mixture withdrawn from the top of the chilling chambers,and lowering the temperature of the combined mixture to substantiallythe temperature oi the Withdrawn chilled mixtlre from the top of thechilling chambers by reducing the hydrostatic head on the mixture.

^ 23. In a process for dewaxing oils the steps comprising mixing waxyoil with a. volatile liquid refrigerant under superatmospheric pressure,passing said mixture into the bottom of chilling chambers connected inseries and maintained at successively lower temperature and pressurelevels by vaporization of said volatile liquid refrigerant under reducedpressure, withdrawing chilled mixture from the top of said chillingchambers and commingling said withdrawn mixture with the mixture to bechilled entering the bottom of said chilling chambers, said admixturebeing in quantities suilicient to reduce the temperature of the combinedmixture to approximately 3 F. higher than the temperature of the chilledmixture withdrawn from the top of the chilling chambers and reducing thetemperature of the combined mixture to substantially the temperature ofthe chilled mixture withdrawn from the top of the chilling chambers bylessening the hydrostatic head on the 'mixture and. vaporizing a portionof the volatile liquid refrigerant.

DAVID R. MERRIIL.

